The non-self starting musical box governor.

Most governor problems are attributable to wear.  The mechanics of wear
is a complex study but much easier to understand when considering wear
between the surfaces of the hard brass worm wheel (sometimes called
a bay-leaf wheel because of its shape in profile) and the hardened and
polished steel worm (also called the endless).

In pristine condition the teeth of the worm wheel are straight, angled
forward and parallel with the mating surface of the endless.  The
spiral shape of the endless is a flat surface with a straight line of
contact between the two components.  As the worm rotates its tooth
pushes the endless upwards.  The endless acts like an inclined plane
that slides sideways across the face of the tooth causing the endless
to rotate.

The air vanes (or butterfly) are the main cause of friction between the
worm tooth and the endless.  As the vanes rotate, they push air away to
impede rotation.  It is this resistance that places the load on the
worm teeth and causes wear.

Now consider how a worm tooth engages and disengages with the endless.
As one tip disengages another engages the endless.  A tooth moves in a
straight line of contact towards and away from the axis of the endless,
just like a piston and it is this part of the tooth that wears.

When new, the depth of engagement between worm and endless is not
critical or sensitive.  As wear takes place it does so in two ways.
First it changes the profile of the tip of the worm teeth from straight
to rounded.

Second, it wears a microscopic step in the endless.  That step can be
the most critical point of contact.  If the worm tooth is set in too
far it sits on the step, if set out too far it has less leverage on the
worm.  Even if set exactly as before, the degree of wear and changes in
profile due to wear can make the governor a non-self starter.

Another critical wear point is the top of the endless where it sits
against the jewel.  It should be dome-shaped but as wear takes place it
gets flattened.  It also wears the jewel.

Probably the worst thing to do is to start by dismantling the governor.
So what should be done?  It is always best to read an acknowledged work
such as Bulleid's "Cylinder Musical Box Design & Repair", Webb's "The
Cylinder Musical Box Handbook", Ord-Hume's "Restoring Musical Boxes" or
any of the other recognised books on the subject.

The next step is to examine visually the worm and endless for wear
but do not make any adjustments to the setting of the lower bearing.
A magnifying glass is normally sufficient to detect wear.  I have also
used a high-resolution digital camera, transferred the image to the
computer and then used he 'magnifying' feature to examine for wear.

With the governor assembly removed from the bedplate (after all
due precautions are taken about letting the spring motor run down
completely and possibly removing the comb) it is best to start with
cleaning.  An ultrasonic bath and propriety clock/watch cleaning
and rinsing fluids are ideal.  Spray-type cleaners may do the job
(I leave others to comment) but overuse can cause problems.  These
propriety cleaners often have some form of lubricant.

Manual cleaning should never be made with an abrasive material.
If components need to be polished or lapped, they must be cleaned
subsequently to remove all traces.  Clean the bearings with a cherry
stick or toothpick or peg wood and use just a small drip of oil for
each bearing.  If the governor fly rotates freely under light upward
pressure on the first gear, the wear problem is effectively resolved.
If not, continue as follows.

In the cleaned state, it is easy to check bearing wear.  A pair of
tweezers and a little jiggling back and forth may show the extent of
wear but it is important to remember that bearings can take considerable
wear before affecting governor performance.  Therefore, it is best not
to re-bush bearings until all other aspects of wear rectification has
been carried out.

Start with the endless and jewel.  If the endless has worn a depression
in the jewel rotate the jewel slightly.  It may result in a free running
endless with nothing more required.  It is also possible to lap the
face of the jewel flat again.  Both are practical options.

The top spigot of the endless should be dome-shaped.  If not, take
some advice on how to lap, polish and clean the top.  I have used a
hand-operated mini-drill, clamping the endless gently in the chuck and
using the finest of abrasive papers (1200 grade) to re-profile the
dome.  The mini-drill with a small buffing wheel can then be used to
polish the dome.  Make sure that the whole endless is then cleaned.

It might be easier, though, to inspect the jewel first for wear.  Again,
check the upward pressure on the first gear.  If that fails turn your
attention to the worm wheel.

Even with a worn governor assembly, cleaning, light lubrication and
slight adjustment to the lower gearing may allow the governor to
continue working.  If badly worn, the worm teeth can be re-profiled
back to a straight line again at the original angle.  A skilled
watchmaker can make an easy job of this.  What can the amateur do?

With some trepidation but success, I have dressed each face of the
worm teeth by hand.  The professional may warn against this but a fine
'needle' file lightly stroked across the face of each tooth in turn
may do the job.  It is worth a try and inexpensive.

I have also used a combination of file and a scalpel with chisel-shaped
blade.  Gently stroke the blade up the filed edge to smooth out the
finest of file marks.  The worm wheel has a flat face on one side and
is angled on the other face.  The scalpel blade can also be used to
gently 'pare off' the angled face along the line of the active edge of
the tooth.

If the worm wheel still does not work properly then perhaps the endless
needs to be re-lapped.  Mounted between centres in a watchmaker's lathe
(stationary of course), it is possible to polish the worm.

Old-fashioned page cord or the like can be wound a turn or two around
the endless.  If slightly waxed and impregnated with a lapping compound
(jewellers rouge, metal polish) 20 minutes or so of pulling and pushing
plus turning the endless may do the job by diminishing or lapping out
the step in the endless; then clean thoroughly.

To recap:

- Remove the governor assembly, inspect, clean and lubricate.
- Rotate the jewel and reassemble.  If it does not solve the problem,
- check the dome-shape of the endless and reassemble.

Only then should any attempt be made to adjust the bottom bearing.  In
doing so, it may be better to move it very slightly away from the worm
wheel first, i.e., away from where the step existed.  If that fails:

- Check and reshape the worm wheel as described.  If that still fails,
- lap and polish the endless.

If all this fails the help of an expert may be needed and replacement
worm and wheel required.

Lubrication: Never use grease.  Clock/watch oil or gun oil is ideal but
do not over-lubricate.  The active part of the lubricant is not visible
oil but the invisible film that, like the meniscus in the surface of
water, stretches over the entire surface.  This film of oil enters the
microscopic interstices of the polished surfaces and acts as a barrier
to prevent/limit metal-to-metal contact.

Paul Bellamy

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